The present invention relates to a dredge cutterhead used to remove material from harbors, shipping channels, and other marine environments and mining operations.
Dredge cutterheads are generally hemispherical with a multiplicity of hard rock cutting teeth or replaceable edges projecting outwardly from helical support arms or blades disposed about the hemispherical surface of the cutterhead. An example of such a dredge cutterhead is disclosed in Bowes, Jr., U.S. Pat. No. 4,891,893. The cutterhead has a hub which fits around a shaft that provides the torque for turning the cutterhead in its operation of dredging. The cutterhead encounters all kinds of materials, including rock, sand and clay which must be removed from the bed being dredged.
Conventional cutterhead arms are shaped to minimize wear, but are not designed to move material. However, one of the problems encountered by cutterheads is that the material loosened by the cutting teeth must be directed into a suction pipe in order to be removed from the bottom of the waterway. As the cutterhead moves across the waterway bottom, the cutting teeth dig below the bed to loosen material. Unfortunately, a substantial portion of the material loosened by the cutting teeth does not reach the suction mouth, which is generally located adjacent to the lower side of the ring of the cutterhead. Instead, some of the loosened material quickly falls off the trailing edge of the digging arm and tumbles onto the following arm. When the cutterhead is operated at a steep ladder angle (for example as shown in FIG. 1), the loosened material remains near the hub end of the arm, and prevents admission of new material into the cutterhead.
The result is that the finished bed depth provided by the dredge cutterhead is often limited to the depth of the mouth of the suction pipe, rather than the depth of cut achieved by the cutting teeth. Since the dredge cutterhead itself is large and is often operated at an inclined ladder angle during use, the difference between the depth of cut achieved by the cutting teeth and the depth of the suction mouth may be as large as three to four feet. Accordingly, in order to achieve a specified finished bed depth, it is often necessary to cut into the bed substantially below the specified finished bed depth so that a sufficient amount of material may be removed. This results in additional time and effort needed to achieve a specified finished bed depth.
One attempt to direct material inwardly from the cutterhead to the suction pipe is disclosed in Fray, U.S. Pat. No. 2,090,790, which discloses a rotary cutter comprised of a plurality of blades. The body of each blade extends substantially in the line of a helix taken around the center of rotation, and the cut material accumulates within the space defined by the cutting blades, to be discharged into the usual suction pipe. Each blade provides a plurality of rib formations which are intended to propel movement of the earth or other materials being handled to the suction pipe.
Another attempt to move dredged material is disclosed in Shiba et al., U.S. Pat. No. 4,702,024, which discloses scoop-in plates 7 coupled between helical vanes 3 and a ring 24. Earth and sand are scooped in by means of the scoop-in plate 7 so as to be directed toward the suction tube 5. However, the vanes themselves do not capture material so as to move the material toward the scoop-in plates.
Another dredge cutterhead has involved adding at the upper portion of the arm a wall at a sharp angle following a conventionally shaped cutterhead arm. The lower portion of the arm was shaped like that of a conventional cutterhead. Cross-sections of the arm of this prior art cutterhead are shown in FIGS. 10A-10D, which correspond to the locations of the cross-sections 6A-6D of the present invention. This arm shape caused dredged material to accumulate in the upper portion of the arm at the sharply angled juncture between the leading edge of the arm and the rear wall. This resulted in material jamming the interior of the cutterhead, and prevented the cutterhead from removing dredged material.
What is therefore desired is a dredge cutterhead that efficiently captures the loosened material within the cutterhead, that moves the dredged material to the mouth of the suction pipe, that supports and allows for the easy replacement of standard cutting teeth, and that is capable of withstanding the extreme forces encountered during dredging without breaking or becoming deformed.
The present invention overcomes the aforesaid drawbacks of the prior art by providing an improved dredge cutterhead.
In a first aspect of the invention, a dredge cutterhead comprises a hub, a ring, and a plurality of helical arms interconnecting the hub and the ring. Each of the helical arms has a leading edge for attachment of cutting teeth, a trailing edge, and a trough portion therebetween. The arm is shaped such that the net force exerted on material in the trough portion pushes the material toward the ring substantially along the center of the trough portion. By xe2x80x9cnet forcexe2x80x9d is meant the force exerted on the material by the combination of gravity, buoyancy and centrifugal force.
In a second related aspect of the invention, a dredge cutterhead comprises a plurality of helical arms, the helical arms interconnecting a hub and a ring. Each of the helical arms has a leading edge for attachment of cutting teeth, a trailing edge, and a trough portion therebetween. Each arm has a degree of curvature near the ring of at least 10%.
These aspects of the invention provide several advantages. By shaping the arm so that the net force directs material toward the ring, the arm acts like a pump vane to move material efficiently toward the mouth of the suction pipe. In addition, by providing a relatively large degree of curvature near the ring, the trough portion of the arm is shaped so as to retain the dredged material within the cutterhead as it flows toward the suction pipe. Material loosened by the cutting teeth flows along the trough portion of the arm and toward the ring. The trough portion prevents the loose material from spilling over the trailing edge of the arm and out of the interior of the cutterhead. The cutterhead thus improves the efficiency of dredging and achieves a deeper finished bed depth for a given depth of cut.
In another aspect of the invention, a dredge cutterhead comprises a hub, a ring and a plurality of helical arms interconnecting the hub and the ring. Each of the helical arms is capable of supporting a plurality of cutting teeth. An annular channel is defined by the ring for retaining loosened material.
This aspect of the invention also serves to facilitate movement of loose, dredged material from the interior of the cutterhead into the suction pipe. Material loosened by the cutting teeth is transported along the arms toward the ring. Once the material enters the ring, the channel retains the loose material. Thus, notwithstanding the rotation of the cutterhead, the loose material remains inside the interior portion of the ring until it is removed by the suction pipe.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.